Can be found here: http://talentedanimals.com/blog/should-joe-breed-his-dogs/
Joe lives on a completely isolated island where he has the only dogs—a nice, happy, healthy, beautiful, unrelated adult male and female. Joe asks everyone on the island, and 4 of them would really like a puppy and are committed and capable of providing a great home and life. Should Joe breed?
NO! Joe should NOT breed because he might produce more than 4 puppies. It is better to let the species go extinct than risk having a surplus.
YES! Joe should breed so that there are future dogs, 4 of whom have great homes. If there are more than 4 puppies, he should place the healthiest, nicest, best structured puppies in the 4 homes, house any extras humanely (in a shelter or with Joe) until a home becomes available or they die of old age.
YES! Joe should breed so that there are future dogs, 4 of whom have great homes. If there are more than 4 puppies, he should place the 4 healthiest, nicest, best structured puppies in the 4 homes, and try to place the others, but if after all reasonable efforts have been expended there remain any surplus puppies, their lives should be ended as quickly and painlessly as possible.
Which of these do you believe is the right choice and why?
(Of course, this is not intended to be read literally—it is ridiculously inaccurate and oversimplified. And I am sure many people will point out the many complications that prevent this question from being applied to reality… It is intended as a thought experiment—a small isolated question to think about that might help to clarify an underlying core notion. In my opinion, anyone who is going to contribute to discourse on the topics of breeding and rescue and reducing shelter populations ought to have thoroughly considered this question.)